The sex scandal has splashed salacious details and allegations of wild parties at Berlusconi's villas across newspaper front pages for weeks and drawn the ire of the Catholic Church.
Though no stranger to legal cases, this is the first judicial action against the three-time premier and media billionaire to impugn his personal conduct, rather than his business dealings. The case raises questions about Berlusconi's ability to govern effectively under mounting legal pressure, and comes at a time when he has been weakened by a fight with an ex-ally.
Prosecutors allege Berlusconi, 74, paid for sex with the Moroccan girl, nicknamed Ruby, who has since turned 18, then used his influence to get her out of police custody when she was detained for the unrelated suspected theft of euro3,000 ($4,103). They allege that he feared her relationship to him would be revealed.
Ruby was released into the custody of a Berlusconi aide, who also is under investigation with two other confidantes.
Paying for sex with a prostitute is not a crime in Italy, but it is if the prostitute is under 18. The age limit was raised from 16 in 2006 during a campaign against underage prostitution by a previous Berlusconi government.
Prosecutors are seeking an immediate trial - a sped-up procedure that would skip the preliminary hearing - because they believe they have sufficient evidence against the premier. The have forwarded a 782-page document to Judge Christina Di Censo to back up their indictment request.
Speaking at a news conference in Rome, Berlusconi said the prosecutors had "offended the dignity of the country" with a smear campaign and groundless allegations.
"It's shameful, really. It's shameful and disgusting," he said of the prosecutors' actions.
"I wonder who's going to pay for these activities, which, in my humble view, only have a subversive aim," Berlusconi added.
Berlusconi said prosecutors had smeared not just his name but that of Italy. He insisted he has only been at the service of his nation.
Both Ruby and Berlusconi have denied having sexual relations, although she has said Berlusconi gave her euro7,000 ($9,550) on their first meeting.
The child prostitution charge carries a possible sentence of six months to three years; the abuse of influence charge, which experts say is more dangerous for Berlusconi, carries a possible sentence of four to 12 years.
In response to that charge, the premier's supporters say he made the call to Milan police only to avert a diplomatic incident because Berlusconi believed at the time that the girl was the niece of Egyptian President Hosni Mubarak. His defense maintains the case should be handled not by the Milan prosecutors but by a special tribunal set up to deal with alleged offenses committed by public officials.
"I have intervened as prime minister, because I was worried that there could be an international diplomatic incident," Berlusconi told reporters Wednesday.
Di Censo, the judge, must now decide whether to dismiss the prosecutors' request or go ahead with a trial - which would add to Berlusconi's already substantial legal worries. A decision is expected within two weeks, just as two unrelated trials and one preliminary legal hearing are about to resume in Milan. These corruption trials are resuming after Italy's Constitutional Court watered down a law that had briefly shielded the premier.
Parliament, in which Berlusconi controls a slim majority, tried to derail the investigation by saying Milan prosecutors don't have jurisdiction and rejecting their request to search Berlusconi's properties for evidence. Chief Milan Prosecutor Edmondo Bruti Liberati, however, said the crime was not committed in the exercise of Berlusconi's duties.
"This is not an act that can be ascribed to his office," he told reporters.
He said prosecutors will not seek to use as evidence a handful of wiretaps of phone calls involving Berlusconi, which would require parliamentary approval, saying they ultimately were "not relevant."
Ruby herself is under investigation for allegedly misidentifying herself when she was held by police for pickpocketing, Bruti Liberati told reporters.
Documents now in the hands of the judge include hundreds of pages of wiretaps of conversations among women at Berlusconi's parties that have been previously leaked to the press.
In some purported conversations, Berlusconi's mansion is described as a brothel with topless girls dancing around; the premier himself is described as a "caricature" by one guest and as having gained weight and having become ugly by another. Other published wiretaps have a woman identified as Ruby saying that Berlusconi was willing to pay for her silence.
Polls suggest the damage to Berlusconi - who was last elected in 2008 to a five-year term - has been limited, and his supporters remain as devout as ever in a sign of Italy's political polarization.
"His popularity is down, but not out," said analyst Roberto D'Alimonte, a professor of political science at Rome's LUISS university. "One of the main reasons is a lack of clear alternative. On the other side, there is not a single credible coalition, there is not a single credible leader and not a single credible program."
Berlusconi's supporters insist the case represents an invasion of privacy, and say the prosecutors should direct their energies elsewhere. About 100 Berlusconi supporters demonstrated Wednesday outside the Milan courthouse, waving Italian flags and holding banners that read "Silvio Must Overcome."
"I am here to defend Silvio, who has done so much for us," said Anna Maria Selvia, a retiree in her 70s, denouncing the scandal's raunchy tales.
While this is the first legal case to touch on his private life, it is not the first sex scandal that has engulfed the premier.
In one case, Patrizia D'Addario, a self-described call girl, said she spent the night with Berlusconi when Barack Obama was elected president. She later gave purported tapes of her encounter with Berlusconi to an Italian magazine.
His second wife, Veronica Lario, announced in 2009 she was divorcing him, citing Berlusconi's purported fondness for younger women. Berlusconi has made no apologies for his lifestyle but has denied ever paying for sex.
Berlusconi's legal worries also include several cases that have been recently unfrozen by the Constitutional Court.
He is charged in a tax fraud case relating to his Mediaset media empire, and charged with bribery in another case. Another tax fraud case, but pertaining to more recent events than the ongoing Mediaset trial, will continue with a preliminary hearing next month.
Berlusconi has always denied wrongdoing in the many cases involving his media holdings, and has always either been acquitted or seen the statute of limitations expire - something that is considered likely in the two trials under way. He has long contended he is the victim of a political vendetta orchestrated by what he says are left-leaning prosecutors intent on ousting him.
"I'm not worried in the slightest," Berlusconi said of the prostitution case. "I am a wealthy gentleman who can spend the rest of his life building hospitals for children like I've always wanted to."
Rizzo reported from Rome.